This study describes histologic and ultrastructural studies of skeletal muscle lesions present in pigs fed a semisynthetic diet deficient in selenium and vitamin E for 13 to 59 days. Major alterations observed consisted of hyaline degeneration of the muscle cells, with subsequent macrophagic invasion and muscle cell regeneration by myoblastic proliferation, fusion and differentiaton into fibers with mature myofibrils. BIBLIOGRAPHIC REFERENCES: Van Vleet, J.F., Ruth, G.R., and Ferrans, V.J.: Ultrastructural alterations in skeletal muscle of pigs with selenium-vitamin E deficiency. Am J Vet Res 37: 911-922, 1976.